Migrate <cr-dialog> from PaperDialogBehavior to native <dialog>.

chrome/browser/resources/settings/about_page/channel_switcher_dialog.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview 'settings-channel-switcher-dialog' is a component allowing the
  * user to switch between release channels (dev, beta, stable). A
  * |target-channel-changed| event is fired if the user does select a different
  * release channel to notify parents of this dialog.
  */
@@ skipping 37 matching lines @@
 
     this.browserProxy_.getCurrentChannel().then(function(channel) {
       this.currentChannel_ = channel;
       // Pre-populate radio group with current channel.
       this.$$('paper-radio-group').select(channel);
     }.bind(this));
   },
 
   /** @override */
   attached: function() {
-    this.$.dialog.open();
+    this.$.dialog.showModal();
   },
 
   /** @private */
   onCancelTap_: function() {
     this.$.dialog.close();
   },
 
   /** @private */
   onChangeChannelTap_: function() {
     var selectedChannel = this.$$('paper-radio-group').selected;
@@ skipping 45 matching lines @@
     };
   },
 
   /** @private */
   onChannelSelectionChanged_: function() {
     var selectedChannel = this.$$('paper-radio-group').selected;
 
     if (selectedChannel == this.currentChannel_) {
       this.shouldShowButtons_ = null;
       this.warning_ = null;
-      this.$.dialog.notifyResize();
       return;
     }
 
     if (settings.isTargetChannelMoreStable(
         this.currentChannel_, selectedChannel)) {
       if (loadTimeData.getBoolean('aboutEnterpriseManaged')) {
         this.updateWarning_(
             'aboutDelayedWarningTitle',
             'aboutDelayedWarningMessage',
             'aboutProductTitle');
         this.updateButtons_(true, false);
       } else {
         this.updateWarning_(
           'aboutPowerwashWarningTitle', 'aboutPowerwashWarningMessage');
         this.updateButtons_(false, true);
       }
     } else {
       this.updateWarning_(
         'aboutUnstableWarningTitle',
         'aboutUnstableWarningMessage',
         'aboutProductTitle');
       this.updateButtons_(true, false);
     }
-    this.$.dialog.notifyResize();
   },
 
   /**
    * @return {boolean}
    * @private
    */
   shouldShowWarning_: function() {
     return this.warning_ !== null;
   },
 });